robertf, you`re right with another makes:smilelol:
ek5usmc: this is the diagnostic method, developed by a lot of cases followed, and mine:
1)Door lock button remains open or closed while the rest change from one position to the other, most frequently rear passenger door: lock actuator.
2)Unlocked door don't opens, lock button seems to be in the correct position.
If You can open the door by pulling up lock button from inside the Disco, or forcing the unlock position with the key, from outside: "p..o resortito" (little f...spring)
If You modify rods length in order to correct this situation with less work, may be You will have success... until temperature or position of the vehicle changes....
Regards